The present invention relates to an integrated circuit having a power transistor and a circuit arrangement. The circuit arrangement functions in a temperature dependent manner and is thermally coupled to the power transistor.
An overtemperature circuit is described in German Patent No. 195 19 477 in which the power transistor is continuously limited at high temperatures. If the acceptable base temperature of a surface-mounted power transistor is below the trip threshold of the overtemperature fuse, a one-time entry into this range by high self-heating must not result in the melting of the base-side solder layer; however a repeated operation must indeed do so. For that reason it is desirable to provide appropriate xe2x80x9ctripping strategies.xe2x80x9d
In contrast, an advantage of the integrated circuit according to the present invention is that it ensures overtemperature protection for power transistors at temperatures of about 200xc2x0 C. with high precision, thus reliably protecting the component while not constricting its range of use and being suitable for low base temperatures (in surface-mounting). The provision of a first latching circuit results in reliable functioning of the integrated circuit even with variable inductive loads. Thus, the same protective circuit can be used for variously dimensioned inductive loads that are operated via the power transistor to be protected.
It is advantageous if, after the component temperature, for example, the temperature of the base-collector transition of the power transistor, has exceeded an upper temperature threshold and the first latching circuit has disconnected the power transistor, the power transistor cannot be reactivated after falling below the upper temperature threshold until after an edge change has taken place at the base terminal. Particularly in the malfunction of long make-times, i.e., extended times of activation of the power transistor via the base terminal, it is ensured that the base temperature never exceeds an upper limit lying below the upper temperature threshold of the component temperature.
If, in addition, the integrated circuit has a spark suppression component, a break spark occurring under inductive loads can be advantageously suppressed in the event of an overtemperature disconnection. Such a break spark, for example, on the secondary winding of an ignition coil would otherwise endanger the operational reliability of the circuit, since firing pulses may only occur at defined points in time in the ignition area, particularly in motor vehicle applications.
The provision of a control transistor makes it possible to couple the latching circuit to the power transistor in a simple manner.
The advantage of a second latching circuit, particularly with high-frequency activation of the power transistor, is that a reclosing of the power transistor after an overtemperature disconnection is not possible until the component temperature has fallen below a lower temperature threshold.
Falling below the lower temperature threshold can be detected in an advantageous manner by a second temperature sensor which, for example, is optimized in a lower temperature range.
In an advantageous manner, the output of the first latching circuit is connected to the base of a transistor, the collector current of which, for example, triggers a change in the base current of the power transistor via the control transistor.
The first and/or second latching circuit can be implemented in a simple manner as an RS flipflop circuit.
If the first temperature sensor is configured as a sensor transistor, the base-emitter channel of which is interconnected with a temperature-dependent sensor resistor with a positive temperature coefficient, then high component temperatures over 200xc2x0 can be reliably detected.